This activity allows students to use models of Earth, the Sun, and the Moon to discover why moon phases occur. Students use a Styrofoam ball to represent the Moon, which will be lit by a single light source in the classroom, to observe how different portions of the ball are illuminated as they hold it in various positions. They create a complete series of phases matching the appearance of the Moon. And they relate moon phases to the positions of Earth and the Sun.

What Students Will LearnStudents will be able to state the order of the moon phases from one full moon to the next and to demonstrate how the position of the Moon relative to Earth creates moon phases.

Materials

Light bulb on a stand or clamp (or lamp with its shade removed)

Extension cord

Styrofoam balls or light-colored spheres

Pencils

Before the ActivityCollect enough Styrofoam balls to distribute one to each student. Clear space for students to stand and move about as they work through this activity. Check that the lamp or light bulb for the model Sun works properly and that it can be placed in the front of the classroom where everyone can see it. The classroom will need to be completely dark for this activity. This activity requires 1 to 2 class periods.

Scientific Concepts The observed phase of the Moon is determined by its position relative to Earth and the Sun. The changing portion of the Moon's sunlit side that we see throughout the month creates for us the phases of the Moon. In a 28-day period the Moon swells from the new Moon, through the crescent, to the first quarter, the "gibbous," and then the full Moon, before waning to the new Moon again. The Moon's orbit takes it from a position between Earth and the Sun--the new Moon--to the opposite side of Earth from the Sun--the full Moon.

Setting the StageFocus students' attention on patterns of change. Ask students what things they know to repeat again and again. Then explain that moon phases occur repeatedly because of the configuration between the Sun, Earth, and the Moon. These bodies change their relative position in complex ways night by night and month by month, affecting what we see in the sky from our viewpoint on Earth. Explain that students will model the pattern of moon phases.

The Activity

Work with students to review the order of the phases from one full Moon to the next.

Explain that to understand the phases of the Moon students need to look at models of Earth, the Moon, and the Sun. Place the lamp in front of the classroom. (Remind students to practice safety near the hot light bulb and electrical cord.) Have students stand in a semicircle facing the lamp. Explain that the lamp represents the Sun and that each of their heads represents Earth, with their noses being their hometown.

Ask students to stand so it is noontime in their hometown. If disagreement occurs, have students discuss this until they agree that noon is when their noses are pointed toward the model Sun. Ask students to stand so it is midnight. (They should turn to face away from the model Sun.) Then ask them to stand so it is sunrise and sunset. (To stand properly, students must be able to rotate their heads from right to left, with their right shoulders moving forward.) Practice the ideas of sunrise, noon, midnight, and sunset until you sense that the students have a good understanding of these relative positions.

Distribute one Styrofoam ball for the model Moon to each student. Have students stick a pencil into the ball to make it easier to hold as well as observe the phases of the model Moon. Ask students to hold the model Moon at arm's length. Allow time for them to explore how the model Sun's light reflects off the model Moon as they place it in different positions around their heads.

Choose one of the moon phases and ask students to find where that phase occurs in the Moon's orbit around Earth. (The first quarter is a good phase to start with.) Encourage students to compare their results and discuss differences. If one student has the correct position, ask this student to state why it is so. Then check to see whether other students understand what to do; see if they all are standing in the same position.

Have students model the other moon phases: the full Moon, the third quarter Moon, and the new Moon. As students learn where to hold the Styrofoam ball for each phase of the Moon, challenge them to determine the direction that the Moon travels around Earth to create the phases in the correct order. (This can be demonstrated by moving the ball from right to left around the head.)

Allow time for students to experiment with the movement of the Moon. Have them work together to draw a diagram of the Moon's changing position in order to create each phase, and to record on the diagram what causes the phases of the Moon. (The spinning Earth allows us to observe the Moon rising and setting each day, but this spinning does not affect the phase of the Moon. The changing proportion of the Moon's sunlit side that we see as the Moon orbits Earth causes the moon phases.)

See that students check their positions for the model Moon against those in a diagram of the moon phases.

Lead a class discussion in which students can express their new understandings about the phases of the Moon. Then give students the opportunity to record their new understandings in a science journal or, if they wish to be more creative, in a story, poem, or essay.

Tips and SuggestionsThis activity works best in a dark room with a bright light. Leave time to prepare if your classroom is not easily darkened or if a bright light is not easy to find. Dark coverings such as plastic garbage bags work well to block light from windows. An overhead projector can work as the light source.

Because the visualization in this activity can be difficult for some students, consider doing this activity with a smaller group while the rest of the class works on a moon phase chart or another project, or do this activity more than once. Students usually observe that their own shadows cover the model Moon when it is opposite the light source, simulating a moon eclipse during the full moon phase. Ask students to hold the model above or below the shadow of their heads, and ignore the eclipse for the time being.

Before doing the activity, ask the class to list possible explanations for the phenomena of moon phases. Try to avoid making comments on the validity of the theories offered. Ask students to write down their own explanations, based on what they have heard. After the activity, ask students to rewrite their explanations for moon phases and discuss any changes from their previous ideas. Encourage students to do this activity at home with their families or to model the moon phases for younger students and then write about their results.

Before doing the activity, ask the class to list possible explanations for the phenomena of moon phases. Try to avoid making comments on the validity of the theories offered. Ask students to write down their own explanations, based on what they have heard. After the activity, ask students to rewrite their explanations for moon phases and discuss any changes from their previous ideas. Encourage students to do this activity at home with their families or to model the moon phases for younger students and then write about their results.